An acquaintance of mine asked me this question yesterday. And since I have been going through bouts of blogger's (as opposed to writer's) block, I thought I might as well use this question as a subject for the blog. If this is the frustration you experience, I'm not sure this'll help you find a solution. I'm writing this post out of sheer admiration of your problem. Yep, I'm clueless about the problem too, and at the end of this post, I'd know if what I suggest really works.
For starters, I think one should ask himself what does he want to achieve out of running a blog. For me, it's a training ground. I use the blog to strip my mind of all its mess, so that I can go back to writing ad copy (which happens to be my Brittania brown bread earner these days)afresh. So by publishing this entry, I deprive myself of these lame thoughts when I write copy subsequently. Works for me.
One should remember that writing a blog entry is also like writing an essay in school. A blog entry is more than just a set of random words. Together, the words should represent a single thought. So if 'If your name was homework, I'd be doing you on my desk right now.' follows, 'I'd hate to have a kid like me.', you'd be killing two jokes, without a thought. You get the drift, right?
One should always write a blog responsibly, because once you upload a piece, you stand to create an impression. Even a good one, sometimes. But then, just like driving under the influence of alcohol wont cause accidents in the back seat, writing under the influence of testosterone wont result in you laughing all the way to the bed. It may however, land you a writing job in San Fernando valley. So write at your own risk.
If you are trying to cater to an audience, be sure to write about a subject they can relate to. Waxing eloquent about some movie of the 60s that no one has watched, by a famous director nobody acknowledges today will get you neither hits, nor comments. Here's the proof. The only solution to this is back-linking to your previous posts, and the previous link is self-explanatory.
Speaking of the audience which is global, be realistic of the response you'll get. By marooing a PJ in Hinglish, don't expect a blogger in Sierra Leone to recommend you on Stumbleupon. He may however appreciate your list of the 10 most 'civil' war strategies of all time.
And most importantly, learn how to end a blog entry appropriately. It helps if you can qualify your headline and summerise your blog entry in the last paragraph. For instance, it may not help me if I choose to close this paragraph by saying "I still have no clue on what to write about on my blog". Suffice it to say, "This exercise was a failure."